If Allah were to punish people for their wrong actions, not a single creature would be left upon Earth. But He defers them until a predetermined time. When their specified time arrives, they cannot delay it for a single hour or bring it forward. ( Surat an-Nahl, 16:61)

Allah leaves behind and brings forward whoever He wills. Being the sole Creator of everything, He has the power to do whatever He wills with anything that exists. He determines the time for every event and, as the actual master of every being and its destiny, predetermines the events of every being's life. When the specified time arrives, what has been ordained takes place, according to His will. Allah calls attention to this fact in the Qur'an, as follows:

Every nation has an appointed time. When their time comes, they cannot delay it a single hour or bring it forward. ( Surat al-A‘raf, 7:34)

No one except Allah knows this appointed time. No leaf falls before its appointed time, and every moment of a living being's life, from its birth to its death, is subject to this divine timing. However, if Allah wills, He can delay or bring forward any event, for the human concept of time being divided into the past, present, and future does not apply to Him. As the Qur'an states:

Do not consider Allah to be unaware of what the wrongdoers perpetrate. He is merely deferring them to a Day on which their sight will be transfixed. ( Surat Ibrahim, 14:42)

No nation can advance its appointed time, nor can they delay it. ( Surat al-Hijr, 15:5)
This being the case, all sincere servants must strive to draw closer to Him, without considering what He has delayed or brought forward, and must be absolutely pleased with what He gives, for, as the verse maintains, “Man is prone to be impetuous...” ( Surat al-Isra', 17:11) We often expect something to take place or to be over at once. Yet, only Allah knows what is best for us and so ordains all events and situations accordingly. What a person thinks might be good may actually be harmful. Thus, a believer should be pleased with whatever Allah ordains.